Hydrocarbons have traditionally been widely used as an energy source due to their relatively low cost in comparison with other types of fuels or electricity. However, waste hydrocarbons such as crankcase oil, spent motor oil, transmission fluid, lubrication dopes and heavy body gear lubes, while generated in abundance during the operation of gas stations, truck stops, and vehicle repair shops, have not proven to be a useful source of energy and are generally discarded. Seemingly, such waste hydrocarbons could provide a valuable source of energy for purposes such as space and water heating if they could be used a fuel.
However, waste hydrocarbons have proven problematic as a fuel source. Conventional fuel oil burners apparently have difficulty gasifying all of the waste hydrocarbon because of varying viscosities of the waste oils and the presence of dirt and other contaminants. Attempts to burn waste oil in conventional fuel oil burners can result in various problems, including the accumulation of carbon (soot) in the fuel burner and the clogging of nozzles leading to the fuel burner.
The complete, both clean and smokeless, combustion of waste hydrocarbons has also proven to be difficult in conventional pressure atomizing burner systems. In the past, attempts have been made to use commercially produced atomizing burner units for burning waste hydrocarbons. Such atomizing burners force compressed air through a spray nozzle as a means for primary atomization of the fuel. However, widely varying viscosities of waste hydrocarbons make combustion unpredictable. For instance, waste hydrocarbons that have been gathered or stored in a common receptacle will invariably be comprised of mixtures of crankcase oil, spent motor oil, transmission fluid, lubrication dopes and heavy body gear lubes. The net effect of varying viscosities of these waste hydrocarbons in an atomizing burner is that the combustion pattern produces significant unburned droplets at the exterior of the combustion flame, and therefore smoke and air pollutants.
Also, if these unburned droplets impinge on cool surfaces, generally less than 600.degree.-700.degree. F., the waste hydrocarbons will not combust but will instead condense and accumulate, causing the combustion chamber to puddle with waste hydrocarbons, resulting in a messy and potentially hazardous situation. For example, it is possible for the accumulated droplets of unburned hydrocarbons to autoignite suddenly, resulting in flash fires or explosions.
Some atomizing liquid fuel burners have been designed with the object of completely burning the hydrocarbons in order to be more energy efficient, as well as avoid the undesired build-up of carbon and fuel droplets inside the combustion chamber. Many of these designs involve the use of two-stage combustion. In the liquid fuel burner described in U.S. Pat. No. 4,504,215 issued to Akiyarna., a thin coat of the fuel coats the inner wall of the fuel carburetor and flows to the rear end of the fuel carburetor, through scattering gaps, and onto the inner wall of a scattering ring. The thin, continuous coat of fuel is pulverized and atomized by the scatter ring. Primary combustion takes place in the combustion chamber, and secondary combustion occurs with a mixture of evaporated fuel and air.
While the two-stage combustion approach generally results in improved overall combustion, the design in the Akiyama patent still can suffer from accumulation of combustible byproducts and soot generation. It is known that combustion byproducts form in the flame and are transmitted downwardly of the combustion flame to cooler surfaces in the combustion chamber, where condensation and accumulation occurs. Some combustion byproducts are combustible and can cause the problems of unburned accumulations and autoignition.
In the liquid fuel burner described in U.S. Pat. No. 3,734,677 to Murase et al., a mixture of atomized liquid fuel and pre-heated air is burned on the surface of a heat-radiant cylinder and the resultant combustion gases are introduced into the interior of the radiant cylinder, where unburned gas is subjected to secondary combustion by contact with heated rods in the cylinder. While this approach recognizes the need for dealing with combustion byproducts, the heated rods are relatively thin, providing only a small surface area. If the heated surface area for causing secondary combustion were larger, it might be possible for greater secondary combustion to occur.
One approach to providing a greater surface area for secondary combustion of combustion byproducts is shown in German Patent No. 25 23 214 issued to Merk. This patent describes an oil burner with a fuel gasifier and atomizer that provides a fine fuel spray and gasifies the fuel with a concentric shell arrangement. The concentric shells comprise nested cylinders or collection plates arranged in the flame region.
While the Merk approach provides an improvement over the heated rod approach because of its greater heated surface area for secondary combustion and/or gasification, the concentric shell arrangement does not take into consideration the shape of a combustion flame. A combustion flame generally has an elongate tapered cylindrical shape; combustion byproducts are believed to form along the entire length of the flame. The concentric cylinders in the Dieter patent are relatively short compared to the length of the flame, with the possible result that combustion byproducts formed in the flame region subsequent to the concentric cylinders are not subjected to secondary combustion.
Accordingly, there is a need for a combustion chamber that, while capable of utilizing waste hydrocarbons, maximizes the efficiency of the produced heat while minimizing waste hydrocarbon condensation in said combustion chamber.